Vite: Fix pnpm support by replacing @storybook/global with window

[IanVS]

Closes #22695

What I did

If we want to use @storybook/global in a virtual module in the vite builder, we'd need to add it to the runtime bundle in order to support pnpm users. Since this is purely preview code, though, we can just use window and avoid the dep entirely.

How to test

Create a pnpm project, add storybook, swap in this change, confirm that stories load. I did that in my own pnpm project and it works well now on 7.0.15.

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]